Growth, structure and properties of magnetron sputtered ultra-thin WTi films
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Growth, structure and properties of magnetron sputtered ultra-thin WTi films A. Le Priol1, 2, E. Le Bourhis1, P.-O. Renault1, L. Simonot1, G. Abadias1, P. Muller2, H. Sik2 1 Institut P’, CNRS-University of Poitiers, SP2MI, Bd Marie et Pierre Curie, BP30179, 86962 Futuroscope Chasseneuil, France 2 Sagem Défense Sécurité, 72-74 rue de la Tour Billy, BP72, 95101 Argenteuil, France
ABSTRACT Refractory metal alloy WTi films were elaborated by magnetron sputtering from an alloyed target (W:Ti ~ 70:30 at%). Film continuity threshold has been determined at 4.5 ± 0.2 nm using in situ surface differential reflectance (SDR) technique. Prior to film continuity, deposition of a continuous interfacial layer is suggested by both in situ and real-time SDR and wafer-curvature techniques. After continuity, WxTi1-x films (9.5 nm thick WTi films) have a body-centered structure with a {110} fiber texture. Composition (x) and microstructure can be tuned varying working pressure. A transition from compressive to tensile residual stresses was observed by ex situ XRD and wafer-curvature methods. Size dependent resistivity is obtained and slightly varies as a function of working pressure.
INTRODUCTION WTi alloy thin films are extensively used in microelectronics for Al, Ag and Au contacts. Adding Ti to the base metal allows for an increase in corrosion resistance of the metallization. Early studies on WTi were reported by Cunningham et al. [1] on the development of a corrosion-resistant refractory metal-Au contact system. WTi is well known for good adhesion [2], electrical and barrier properties [3,4] and serves as diffusion barrier and contact-tosubstrate layer. Properties of W-alloy thin films are closely linked to both elaboration conditions and film thickness [5,6]. Miniaturization of interconnections size requires the use of ultra-thin films, while maintaining the film continuity to provide effective barrier performance. The realtime wafer-curvature and optical spectroscopy monitoring are attractive measurements to characterize the early stages of film growth [7]. In the present study, we report on the film continuity threshold and stress-microstructureresistivity relationship for WTi films. WTi films were elaborated by magnetron sputtering from an alloyed WTi target (W:Ti ~ 70:30 at%). Film continuity has been investigated for a single sputtering condition by coupling in situ and real-time surface differential reflectance (SDR) and wafer-curvature techniques. Ex situ measurements (residual stress using wafer-curvature and XRD methods, electrical resistivity) were performed on 9.5 ± 0.5 nm thick films varying the working pressure.
EXPERIMENT
WTi films have been deposited at room temperature (RT) by planar magnetron sputtering in DC mode using Ar as working gas in a high vacuum system (base pressure ~ 1 x 10-5 Pa). The WTi target used in this study was 7.6 cm in diameter, with a purity of 4N (i.e. 99.99 %), and an average ratio W:Ti equal to 70:30 at% (or 90:10 wt%). Films were deposited on naturally oxidized Si (001) substrates. Th
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